1. Field of the Invention
This invention relates generally to the production of high resolution patterned images and more specifically to the production of high resolution patterned images with polymeric materials which crosslink upon exposure to X-ray or electron radiation.
2. Description of the Prior Art
The production of high resolution patterned images used in the fabrication of miniaturized circuits of devices depends upon the exposure of portions of a resist coated substrate to radiation, e.g., visible light or electrons, which initiates reactions causing the exposed material to become either more or less easily removed with respect to the unexposed material when processed by suitable wet or self development techniques that will be referred to as developers. The exposure may be with a scanning radiation source that sequentially illuminates selected portions of the resist material or with a radiation source that exposes all of a mask transparent to the radiation but covered with a pattern formed by a material opaque to the radiation thus causing selected portions of the resist material to be illuminated. For polymeric materials, the reactions are predominantly crosslinking or chain scission. The former causes the exposed material to become less soluble and the latter more soluble, with respect to the unexposed material, when exposed to a suitable developer. Following photographic terminology, the resists are commonly referred to as negative and positive, respectively. After portions of the resist are removed by development, the now bored substrate portions may be subjected to further processing steps which may remove the substrate by techniques such as chemical etching; plasma etching or ion milling or deposit material by techniques such as ion implantation or diffusion. The processing sequence may be repeated several times, i.e., the crosslinked resist is stripped off, a new resist coating is put down and the processing sequence repeated.
The high energy and short wavelength of electron and X-ray radiation permit the generation of very high resolution patterns. However, the high speed, high resolution negative electron polymeric resists are not entirely suitable as X-ray resists because, while the polymer absorbs an appreciable fraction of the incident electron radiation, the polymer usually does not absorb an appreciable fraction of the incident X-ray energy. A class of high sensitivity and resolution negative electron resists incorporates highly reactive epoxy groups onto polymer side chains to initiate crosslinking. The crosslinking reaction for both electron and X-ray radiation is believed initiated by absorption of the incident radiation, typically by K or L shell absorption, followed by ejection of a high energy electron which may produce other excited electrons. Either, or both, the incident radiation or an excited electron ultimately causes crosslinking via the reactive epoxy group. Since the crosslinking reactions are initiated by absorbed radiation, the smaller absorption for X-rays of polymers containing mainly first and second row elements generally decreases sensitivity compared with sensitivity to electron radiation. Because of the similarity of the processes leading to crosslinking, it has been proposed, J. Electrochem Soc. 121 1500 (1974), to increase the relatively low X-ray absorption and sensitivity X-ray resists by incorporating atoms having high atomic numbers and X-ray absorption into the resist. Poly(vinyl ferrocene) was mentioned as illustrative. Another X-ray resist uses metal containing compositions such as barium lead acrylate in an amorphous state to increase X-ray absorption.